Department of Ophthalmology, Ninth People's Hospital, Shanghai JiaoTong University School of Medicine, Shanghai, 200011, China.
Shanghai Key Laboratory of Orbital Diseases and Ocular Oncology, Shanghai, 200011, China.
J Exp Clin Cancer Res. 2019 Dec 19;38(1):498. doi: 10.1186/s13046-019-1492-5.
The MYCN amplification is a defining hallmark of high-risk neuroblastoma. Due to irregular oncogenes orchestration, tumor cells exhibit distinct fatty acid metabolic features from non-tumor cells. However, the function of MYCN in neuroblastoma fatty acid metabolism reprogramming remains unknown.
Gas Chromatography-Mass Spectrometer (GC-MS) was used to find the potential target fatty acid metabolites of MYCN. Real-time PCR (RT-PCR) and clinical bioinformatics analysis was used to find the related target genes. The function of the identified target gene ELOVL2 on cell growth was detected through CCK-8 assay, Soft agar colony formation assay, flow Cytometry assay and mouse xenograft. Chromatin immunoprecipitation (ChIP) and Immunoprecipitation-Mass Spectrometer (IP-MS) further identified the target gene and the co-repressor of MYCN.
The fatty acid profile of MYCN-depleted neuroblastoma cells identified docosahexaenoic acid (DHA), an omega-3 polyunsaturated fatty acid with anti-tumor activity, significantly increased after MYCN depletion. Compared with MYCN single-copy neuroblastoma cells, DHA level was significantly lower in MYCN-amplified neuroblastoma cells. RT-PCR and clinical bioinformatics analysis discovered that MYCN interfered DHA accumulation via ELOVL fatty acid elongase 2 (ELOVL2) which is a rate-limiting enzyme of cellular DHA synthesis. Enforced ELOVL2 expression in MYCN-amplified neuroblastoma cells led to decreased cell growth and counteracted the growth-promoting effect of MYCN overexpression both in vitro and vivo. ELOVL2 Knockdown showed the opposite effect in MYCN single-copy neuroblastoma cells. In primary neuroblastoma, high ELOVL2 transcription correlated with favorable clinical tumor biology and patient survival. The mechanism of MYCN-mediated ELOVL2 inhibition contributed to epigenetic regulation. MYCN recruited PRC1 (Polycomb repressive complex 1), catalysed H2AK119ub (histone 2A lysine 119 monoubiquitination) and inhibited subsequent ELOVL2 transcription.
The tumor suppressive properties of DHA and ELOVL2 are repressed by the MYCN and PRC1 jointly, which suggests a new epigenetic mechanism of MYCN-mediated fatty acid regulation and indicates PRC1 inhibition as a potential novel strategy to activate ELOVL2 suppressive functions.
MYCN 扩增是高危神经母细胞瘤的一个决定性标志。由于不规则的癌基因调控，肿瘤细胞表现出与非肿瘤细胞不同的脂肪酸代谢特征。然而，MYCN 在神经母细胞瘤脂肪酸代谢重编程中的作用尚不清楚。
采用气相色谱-质谱联用仪（GC-MS）寻找 MYCN 潜在的靶脂肪酸代谢物。实时 PCR（RT-PCR）和临床生物信息学分析寻找相关靶基因。通过 CCK-8 检测、软琼脂克隆形成实验、流式细胞术检测和小鼠异种移植实验检测鉴定的靶基因 ELOVL2 对细胞生长的功能。染色质免疫沉淀（ChIP）和免疫沉淀-质谱联用（IP-MS）进一步鉴定 MYCN 的靶基因和共抑制因子。
MYCN 缺失的神经母细胞瘤细胞的脂肪酸谱鉴定出二十二碳六烯酸（DHA），一种具有抗肿瘤活性的ω-3 多不饱和脂肪酸，在 MYCN 缺失后显著增加。与 MYCN 单拷贝神经母细胞瘤细胞相比，MYCN 扩增神经母细胞瘤细胞中的 DHA 水平明显较低。RT-PCR 和临床生物信息学分析发现，MYCN 通过 ELOVL 脂肪酸延长酶 2（ELOVL2）干扰 DHA 积累，ELOVL2 是细胞内 DHA 合成的限速酶。在 MYCN 扩增的神经母细胞瘤细胞中强制表达 ELOVL2 导致细胞生长减少，并在体外和体内均拮抗 MYCN 过表达的促生长作用。ELOVL2 敲低在 MYCN 单拷贝神经母细胞瘤细胞中表现出相反的效果。在原发性神经母细胞瘤中，高 ELOVL2 转录与有利的临床肿瘤生物学和患者生存相关。MYCN 介导的 ELOVL2 抑制的机制与表观遗传调控有关。MYCN 募集 PRC1（多梳抑制复合物 1），催化 H2AK119ub（组蛋白 2A 赖氨酸 119 单泛素化）并抑制随后的 ELOVL2 转录。
DHA 和 ELOVL2 的肿瘤抑制特性被 MYCN 和 PRC1 共同抑制，这表明了 MYCN 介导的脂肪酸调节的新的表观遗传机制，并表明 PRC1 抑制作为激活 ELOVL2 抑制功能的潜在新策略。
